SOFC hot box components

ABSTRACT

Various hot box fuel cell system components are provided, such as heat exchangers, steam generator and other components.

FIELD

The present invention is directed to fuel cell systems, specifically tocomponents for a solid oxide fuel cell (SOFC) system hot box.

BACKGROUND

Fuel cells, such as solid oxide fuel cells, are electrochemical deviceswhich can convert energy stored in fuels to electrical energy with highefficiencies. High temperature fuel cells include solid oxide and moltencarbonate fuel cells. These fuel cells may operate using hydrogen and/orhydrocarbon fuels. There are classes of fuel cells, such as the solidoxide regenerative fuel cells, that also allow reversed operation, suchthat oxidized fuel can be reduced back to unoxidized fuel usingelectrical energy as an input.

FIGS. 1-9 illustrate a prior art fuel cell system described in U.S.Published Application 2010/0009221 published on Jan. 14, 2010 (filed asSer. No. 12/458,171 and incorporated herein by reference in itsentirety. Specifically, with reference to FIGS. 1, 2A, 2B and 3A, anintegrated fuel cell unit 10 is shown in form of an integrated solidoxide fuel cell (“SOFC”)/fuel processor 10 having a generallycylindrical construction. The unit 10 includes an annular array 12 ofeight (8) fuel cell stacks 14 surrounding a central axis 16, with eachof the fuel cell stacks 14 having a stacking direction extended parallelto the central axis 16, with each of the stacks having a face 17 thatfaces radially outward and a face 18 that faces radially inward. As bestseen in FIG. 3A the fuel cell stacks 14 are spaced angularly from eachother and arranged to form a ring-shaped structure about the axis 16.Because there are eight of the fuel cell stacks 14, the annular array 12could also be characterized as forming an octagon-shaped structure aboutthe axis 16. While eight of the fuel cell stacks 14 have been shown, itshould be understood that the invention contemplates an annular array 12that may include more than or less than eight fuel cell stacks.

With reference to FIG. 1, the unit 10 further includes an annularcathode recuperator 20 located radially outboard from the array 12 offuel stacks 14, an annular anode recuperator 22 located radially inboardfrom the annular array 12, a reformer 24 also located radially inboardof the annular array 12, and an annular anode exhaust cooler/cathodepreheater 26, all integrated within a single housing structure 28. Thehousing structure 28 includes an anode feed port 30, an anode exhaustport 32, a cathode feed port 34, a cathode exhaust port 36, and an anodecombustion gas inlet port 37. An anode exhaust combustor (typically inthe form an anode tail gas oxidizer (ATO) combustor), shownschematically at 38, is a component separate from the integrated unit 10and receives an anode exhaust flow 39 from the port 32 to produce ananode combustion gas flow 40 that is delivered to the anode combustiongas inlet 37. During startup, the combustor 38 also receives a fuel flow(typically natural gas), shown schematically by arrow 41. Additionally,some of the anode exhaust flow may be recycled to the anode feed port30, as shown by arrows 42. In this regard, a suitable valve 43 may beprovided to selectively control the routing of the anode exhaust flow toeither the combustor 38 or the anode feed port 30. Furthermore, althoughnot shown, a blower may be required in order to provide adequatepressurization of the recycled anode exhaust flow 42. While FIGS. 1, 2Aand 2B are section views, it will be seen in the later figures that thecomponents and features of the integrated unit 10 are symmetrical aboutthe axis 16, with the exception of the ports 34, 36 and 37.

With reference to FIG. 1 and FIG. 2A, the cathode flows will beexplained in greater detail. As seen in FIG. 1, a cathode feed(typically air), shown schematically by arrows 44, enters the unit 10via the port 34 and passes through an annular passage 46 before enteringa radial passage 48. It should be noted that as used herein, the term“radial passage” is intended to refer to a passage wherein a flow isdirected either radially inward or radially outward in a generallysymmetric 360 degree pattern. The cathode feed 44 flows radially outwardthrough the passage 48 to an annular passage 50 that surrounds the array12 and passes through the cathode recuperator 20. The cathode feed 44flows downward through the annular passage 50 and then flows radiallyinward to an annular feed manifold volume 52 that surrounds the annulararray 12 to distribute the cathode feed 44 into each of the fuel cellstacks 14 where the cathode feed provides oxygen ions for the reactionin the fuel cell stacks 14 and exits the fuel cell stacks 14 as acathode exhaust 56. The cathode exhaust 56 then flows across thereformer 24 into an annular exhaust manifold area 58 where it mixes withthe combustion gas flow 40 which is directed into the manifold 58 via anannular passage 60. In this regard, it should be noted that thecombustion gas flow 40 helps to make up for the loss of mass in thecathode exhaust flow 56 resulting from the transport of oxygen in thefuel cell stacks 14. This additional mass flow provided by thecombustion gas flow 40 helps in minimizing the size of the cathoderecuperator 20. The combined combustion gas flow 40 and cathode exhaust56, shown schematically by arrows 62, exits the manifold 58 via acentral opening 64 to a radial passage 66. The combined exhaust 62 flowsradially outward through the passage 66 to an annular exhaust flowpassage 68 that passes through the cathode recuperator 20 in heatexchange relation with the passage 50 to transfer heat from the combinedexhaust 62 to the cathode feed 44. The combined exhaust 62 flows upwardthrough the annular passage 68 to a radial passage 70 which directs thecombined exhaust 62 radially inward to a final annular passage 72 beforeexiting the unit 10 via the exhaust port 36.

With reference to FIG. 1 and FIG. 2B, an anode feed, shown schematicallyby arrows 80, enters the unit 10 via the anode feed inlet port 30preferably in the form of a mixture of recycled anode exhaust 42 andmethane. The anode feed 80 is directed to an annular passage 82 thatpasses through the anode recuperator 22. The anode feed 80 then flows toa radial flow passage 84 where anode feed 80 flows radially outward toan annular manifold or plenum 86 that directs the anode feed into thereformer 24. After being reformed in the reformer 24, the anode feed 80exits the bottom of reformer 24 as a reformate and is directed into anintegrated pressure plate/anode feed manifold 90. The feed manifold 90directs the anode feed 80 to a plurality of stack feed ports 92, withone of the ports 92 being associated with each of the fuel cell stacks14. Each of the ports 92 directs the anode feed 80 into a correspondinganode feed/return assembly 94 that directs the anode feed 82 into thecorresponding fuel cell stack 14 and collects an anode exhaust, shownschematically by arrows 96, from the corresponding stack 14 after theanode feed reacts in the stack 14. Each of the anode feed/returnassemblies 94 directs the anode exhaust 96 back into a corresponding oneof a plurality of stack ports 98 in the pressure plate/manifold 90(again, one port 98 for each of the fuel cell stacks 14). The manifold90 directs the anode exhaust 96 radially inward to eight anode exhaustports 100 (again, one for each stack 14) that are formed in the pressureplate/manifold 90. The anode exhaust 96 flows through the ports 100 intoa plurality of corresponding anode exhaust tubes 102 which direct theanode exhaust 96 to a radial anode exhaust flow passage 104. The anodeexhaust 96 flows radially inward through the passage 104 to an annularflow passage 106 that passes downward through the anode recuperator 22in heat exchange relation with the flow passage 82. The anode exhaust 96is then directed from the annular passage 106 upward into a tubularpassage 108 by a baffle/cover 110 which is preferably dome-shaped. Theanode exhaust 96 flows upwards through the passage 108 before beingdirected into another annular passage 112 by a baffle/cover 114, whichagain is preferably dome-shaped. The annular passage 112 passes throughthe anode cooler 26 in heat exchange relation with the annular cathodefeed passage 46. After transferring heat to the cathode feed 44, theanode exhaust 96 exits the annular passage 112 and is directed by abaffle 116, which is preferably cone-shaped, into the anode exhaust port32.

With reference to FIGS. 3A, 3B, the reformer 24 is provided in the formof an annular array 280 of eight tube sets 282, with each tube set 282corresponding to one of the fuel cell stacks 14 and including a row offlattened tubes 284. In this regard, it should be noted that the numberof tubes 284 in the tube sets 282 will be highly dependent upon theparticular parameters of each application and can vary from unit 10 tounit 10 depending upon those particular parameters.

FIG. 3C is intended as a generic figure to illustrate certainconstruction details common to the cathode recuperator 20, the anoderecuperator 22, and the anode cooler 26. The construction of each ofthese three heat exchangers basically consists of three concentriccylindrical walls A,B,C that define two separate flow passages D and E,with corrugated or serpentine fin structures G and H provided in theflow passages D and E, respectively, to provide surface areaaugmentation of the respective flow passages. Because the heat transferoccurs through the cylindrical wall B, it is preferred that the fins Gand H be bonded to the wall B in order to provide good thermalconductivity, such as by brazing. On the other hand, for purposes ofassembly and/or allowing differential thermal expansion, it is preferredthat the fins G and H not be bonded to the cylindrical walls A and C.For each of the heat exchangers 20, 22 and 26, it should be understoodthat the longitudinal length and the specific geometry of the fins G andH in each of the flow paths D and E can be adjusted as required for eachparticular application in order to achieve the desired outputtemperatures and allowable pressure drops from the heat exchangers.

Turning now to FIG. 4A-D, the anode cooler 26 includes a corrugated orserpentine fin structure 300 to provide surface area augmentation forthe anode exhaust 96 in the passage 112, a corrugated or serpentine finstructure 302 that provides surface area augmentation for the cathodefeed flow 44 in the passage 46, and a cylindrical wall or tube 304 towhich the fins 300 and 302 are bonded, preferably by brazing, and whichserves to separate the flow passage 46 from the flow passage 112. Asbest seen in FIG. 4B, a cylindrical flow baffle 306 is provided on theinterior side of the corrugated fin 300 and includes the dome-shapedbaffle 114 on its end in order to define the inner part of flow passage112. A donut-shaped flow baffle 308 is also provided to direct thecathode feed 44 radially outward after it exists the flow passage 46.The cone-shaped baffle 116 together with the port 32 are attached to thetop of the tube 304, and include a bolt flange 310 that is structurallyfixed, by a suitable bonding method such as brazing or welding, to theport 32, which also includes a bellows 311 to allow for thermalexpansion between the housing 28 and the components connected throughthe flange 310. As seen in FIG. 4C, the above-described components canbe assembled as yet another subassembly that is bonded together, such asby brazing.

In reference to FIGS. 1 and 4D, it can be seen that the anoderecuperator 22 includes a corrugated or serpentine fin structure 312 inthe annular flow passage 82 for surface area augmentation for anode feed80. As best seen in FIG. 1, the anode recuperator 22 further includesanother corrugated or serpentine fin structure 314 in the annular flowpassage 106 for surface augmentation of the anode exhaust 96.

As best seen in FIG. 4D, corrugated fins 312 and 314 are preferablybonded to a cylindrical wall of tube 316 that serves to separate theflow passages 82 and 106 from each other, with the dome-shaped baffle110 being connected to the bottom end of the wall 316. Anothercylindrical wall or tube 320 is provided radially inboard from thecorrugated fin 314 (not shown in FIG. 4D, but in a location equivalentto fin 300 in cylinder 304 as seen in FIG. 4B) to define the inner sideof the annular passage 106, as best seen in FIG. 4D. As seen in FIG. 2A,an insulation sleeve 322 is provided within the cylindrical wall 320 anda cylindrical exhaust tube 324 is provided within the insulation sleeve322 to define the passage 108 for the anode exhaust 96. Preferably, theexhaust tube 324 is joined to a conical-shaped flange 328 provided at alower end of the cylindrical wall 320. With reference to FIG. 4D,another cylindrical wall or tube 330 surrounds the corrugated fin 312 todefine the radial outer limit of the flow passage 82 and is connected tothe inlet port 30 by a conical-shaped baffle 332. A manifold disk 334 isprovided at the upper end of the wall 316 and includes a central opening336 for receiving the cylindrical wall 320, and eight anode exhaust tubereceiving holes 338 for sealingly receiving the ends of the anodeexhaust tubes 102, with the plate 308 serving to close the upper extentof the manifold plate 334 in the assembled state.

With reference to FIGS. 2B and 4E, a heat shield assembly 350 is shownand includes an inner cylindrical shell 352 (shown in FIG. 2B), an outercylindrical shell 354, an insulation sleeve 356 (shown in FIG. 2B)positioned between the inner and outer shells 352 and 354, and adisk-shaped cover 358 closing an open end of the outer shell 350. Thecover 358 includes eight electrode clearance openings 360 for throughpassage of the electrode sleeves 211. As seen in FIG. 4E, the heatshield assembly 350 is assembled over an insulation disk 361 the outerperimeter of the assembled array 12 of fuel cells 14 and defines theouter extent of the cathode feed manifold 52. The heat shield 350 servesto retain the heat associated with the components that it surrounds.FIG. 5 shows the heat shield assembly 350 mounted over the stacks 14.

With reference to FIG. 1 and FIG. 6, the cathode recuperator 20 includesa corrugated or serpentine fin structure 362 to provide surfaceenhancement in the annular flow passage 68 for the combined exhaust 62,a corrugated or serpentine fin structure 364 to provide surfaceenhancement in the annular flow passage 50 for the cathode feed 44, anda cylindrical tube or wall 366 that separates the flow passages 50 and68 and to which the fins 362 and 364 are bonded. A disk-shaped coverplate 368 is provided to close the upper opening of the cylindrical wall366 and includes a central opening 370, and a plurality of electrodeclearance openings 372 for the passage of the electrode sleeve 211therethrough. A cylindrical tube or sleeve 376 is attached to the cover368 to act as an outer sleeve for the anode cooler 26, and an upperannular bolt flange 378 is attached to the top of the sleeve 376. Alower ring-shaped bolt flange 380 and an insulation sleeve 382 arefitted to the exterior of the sleeve 376, and a cylindrical wall orshield 384 surrounds the insulation sleeve 382 and defines an inner wallfor the passage 72, as best seen in FIGS. 1 and 6.

With reference to FIG. 7, the components of FIG. 6 are then assembledover the components shown in FIG. 5 with the flange 378 being bolted tothe flange 310.

With reference to FIG. 4A, the outer housing 28 is assembled over theremainder of the unit 10 and bolted thereto at flange 380 and a flange400 of the housing 28, and at flange 402 of the assembly 237 and aflange 404 of the housing 28, preferably with a suitable gasket betweenthe flange connections to seal the connections.

FIG. 9 is a schematic representation of the previously describedintegrated unit 10 showing the various flows through the integrated unit10 in relation to each of the major components of the integrated unit10. FIG. 9 also shows an optional air cooled anode condenser 460 that ispreferably used to cool the anode exhaust flow 39 and condense watertherefrom prior to the flow 39 entering the combustor 38. If desired,the condenser may be omitted. FIG. 9 also shows a blower 462 forproviding an air flow to the combustor 38, a blower 464 for providingthe cathode feed 44, and a blower 466 for pressurizing the anode recycleflow 42. If desired, in an alternate embodiment of the unit 10 shown inFIG. 9 also differs from the previously described embodiment shown inFIG. 1 in that an optional steam generator (water/combined exhaust heatexchanger) 440 is added in order to utilize waste heat from the combinedexhaust 62 to produce steam during startup. In this regard, a water flow442 is provided to a water inlet port 444 of the heat exchanger 440, anda steam outlet port directs a steam flow 448 to be mixed with the anodefeed 80 for delivery to the anode feed inlet port 30.

SUMMARY

An embodiment relates to a cathode recuperator uni-shell including amonolithic assembly comprising a single plate, a top enclosure and abottom enclosure. The cathode recuperator uni-shell is configured sothat a first fluid flows on one side of the single plate and a secondfluid flows on an opposite side of the single plate. The cathoderecuperator uni-shell rests on a column support which provides internalcompression to a column of solid oxide fuel cell stacks.

Another embodiment relates to a fuel cell stack electrical terminalincluding a fuel cell stack support base having a bridging tubeextending through an opening the base and a current collector passingthrough the bridging tube from a fuel cell stack to outside the base.

Another embodiment relates to a method of insulating a fuel cell hot boxfeature including pouring a flowable insulating material into a gapbetween the fuel cell hot box feature and an adjacent feature andallowing the flowable insulating material to solidify.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a prior art fuel cell unit with anintegrated SOFC and fuel processor.

FIGS. 2A and 2B are sectional views showing one half of the prior artfuel cell unit of FIG. 1, with FIG. 2A illustrating the flows of thecathode feed and exhaust gases and FIG. 2B illustrating the flows of theanode feed and exhaust gases.

FIG. 3A is a sectional view taken from line 3A-3A in FIG. 1, but showingonly selected components of the fuel cell unit.

FIG. 3B is an enlarged, somewhat schematic view taken from line 3B-3B inFIG. 3A.

FIG. 3C is a partial section view illustrating construction detailscommon to several heat exchangers contained within the integrated unitof FIG. 1.

FIGS. 4A and 4B are exploded perspective views of the components of ananode exhaust cooler of the integrated unit of FIG. 1.

FIG. 4C is a perspective view showing the components of FIGS. 4A and Bin their assembled state.

FIG. 4D is an exploded perspective view showing the assembled componentstogether with an anode recuperator of the integrated unit of FIG. 1.

FIG. 4E is an exploded perspective view showing the components of thefuel cell stacks, anode recuperator and anode cooler together with aninsulation disk and heat shield housing of the integrated unit of FIG.1.

FIG. 5 is a perspective view showing the assembled state of thecomponents of FIG. 4E.

FIG. 6 is an exploded perspective view showing a cathode recuperatorassembly together with other components of the integrated unit of FIG.1.

FIG. 7 is an exploded perspective view showing the assembled componentsof FIG. 6 together with the assembled components of FIG. 4.

FIG. 8 is an exploded perspective view showing the assembled componentsof FIG. 7 together with an outer housing of the integrated unit of FIG.1.

FIG. 9 is a schematic representation of the fuel cell unit if FIG. 1.

FIG. 10A is an exploded view of an anode exhaust cooler heat exchangerhaving two finger plates according to an embodiment.

FIG. 10B is a photograph of an exemplary anode exhaust cooler heatexchanger of FIG. 10A.

FIG. 10C is a schematic illustration showing axial gas flow entry/exitin an anode exhaust cooler heat exchanger having finger plates.

FIG. 10D is a schematic illustration showing non-axial gas flowentry/exit in an anode exhaust cooler heat exchanger having cap rings.

FIG. 11A is a top cross sectional view of a portion of the anode exhaustcooler heat exchanger of FIG. 10A.

FIG. 11B is a side sectional view of a baffle plate located over theanode exhaust cooler heat exchanger of FIG. 10A.

FIG. 11C is a schematic illustration of a flow director device accordingto an embodiment.

FIG. 11D is a semi-transparent three dimensional view of a baffle platelocated over the anode exhaust cooler heat exchanger of FIG. 10A.

FIG. 11E is a three dimensional view illustrating an anode exhaustcooler heat exchanger and a fuel inlet conduit according to anembodiment.

FIG. 11F is a three dimensional cut-away view of the anode exhaustcooler heat exchanger and fuel inlet conduit of FIG. 11E.

FIGS. 12A-12H are sectional views of a cathode recuperator according toan embodiment.

FIG. 13A is a sectional view illustrating a uni-shell recuperatorlocated on the top of one or more columns of fuel cells according to anembodiment.

FIG. 13B is a sectional view illustrating a uni-shell recuperator andbellows according to an embodiment.

FIG. 14 is a sectional view of a cathode exhaust steam generatorstructure according to an embodiment.

FIG. 15A is a three dimensional cut-away view of a vertical/axial anoderecuperator according to an embodiment.

FIG. 15B is a sectional view illustrating fuel inlet and fuel outlettubes located in a hot box base.

FIGS. 15C and 15D are three dimensional views of embodiments of catalystcoated inserts for the steam methane reformer.

FIG. 16 is a three dimensional cut-away view of an anode flow structureaccording to an embodiment.

FIG. 17A is a three dimensional view of an anode hub flow structureaccording to an embodiment.

FIGS. 17B and 17C are side cross sectional views of an anode recuperatoraccording to an embodiment.

FIG. 17D is a top cross sectional view of the anode recuperator of FIGS.17B and 17C.

FIG. 18A is a three dimensional view of an anode tail gas oxidizeraccording to an embodiment.

FIGS. 18B and 18C are three dimensional cut-away views of the anode tailgas oxidizer of FIG. 18A.

FIG. 18D is a schematic illustration of the top view of a fuel cellsystem showing a cathode exhaust swirl element according to anembodiment.

FIG. 19 is a three dimensional cut-away view illustrating the stackelectrical connections and insulation according to an embodiment.

FIG. 20 is a schematic process flow diagram illustrating a hot boxaccording to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments of the invention provide fuel cell hot box componentswhich improve the fuel cell system performance. Embodiments include ananode exhaust cooler heat exchanger with “finger plates”, a cathoderecuperator uni-shell, a cathode recuperator uni-shell ceramic columnsupport and expansion bellows, a cathode exhaust steam generatorstructure, a pre-reformer tube-insert catalyst, an anode flow structurehub, an anode tail gas oxidizer (ATO) air swirl element, an ATO fuelinjector, and a pour-in outer-insulation and simplified stack electricalterminals.

Anode Exhaust Cooler Heat Exchanger

It is desirable to increase overall flow conditions and rates of thefluids (e.g., fuel and air inlet and exhaust streams) in the hot box.According to the first embodiment, an anode exhaust cooler heatexchanger with “finger plates” facilitates these higher overall flowconditions. An anode cooler heat exchanger is a heat exchanger in whichthe hot fuel exhaust stream from a fuel cell stack exchanges heat with acool air inlet stream being provided to the fuel cell stack (such as aSOFC stack). This heat exchanger is also referred to as an airpre-heater heat exchanger in U.S. application Ser. No. 12/219,684 filedon Jul. 25, 2008 and Ser. No. 11/905,477 filed on Oct. 1, 2007, both ofwhich are incorporated herein by reference in their entirety.

An exemplary anode exhaust cooler heat exchanger 100 is illustrated inFIGS. 10A-10B and 11. Embodiments of the anode exhaust cooler heatexchanger 100 include two “finger” plates 102 a, 102 b sealed onopposite ends of a corrugated sheet 104, as shown in FIG. 10A. Thecorrugated sheet 104 may have a cylindrical shape (i.e., a cylinder witha corrugated outer wall) and the finger plates 102 a, 102 b are locatedon the opposite ends of the cylinder. That is, the peaks and valleys ofthe corrugations may be aligned parallel to the axial direction of thecylinder with the finger plates 102 a, 102 b designed to coveralternating peaks/valleys. Other shapes (e.g., hollow rectangle,triangle or any polygon) are also possible for the sheet 104. The fingerplates comprise hollow ring shaped metal plates which have finger shapedextensions which extend into the inner portion of the ring. The plates102 a, 102 b are offset from each other by one corrugation, such that ifthe fingers of top plate 102 a cover every inward facing recess in sheet104, then bottom plate 102 b fingers cover every outward facing recessin sheet 104 (as shown in FIG. 10B which illustrates an assembled heatexchanger 100), and vise-versa. The shape of each finger is configuredto cover one respective recess/fin/corrugation in sheet 104. The fingersmay be brazed to the sheet 104.

The corrugations or fins of the sheet 104 may be straight as shown inFIGS. 10A and 11 or wavy as shown in FIG. 10B. The wavy fins are finswhich are not straight in the vertical direction. Such wavy fins areeasier to manufacture.

The use of the finger plates 102 a, 102 b is not required. The samefunction could be achieved with the use of flat cap rings or end caps102 c that are brazed to the top/bottom of the fins 104, as shown inFIG. 10D. The advantage of the finger plate 102 a, 102 b design is thatit allows for axial gas flow entry and/or exit to and from the fins 104,as shown schematically by the arrows in FIG. 10C. In contrast, as shownin FIG. 10D, the cap ring(s) 102 c require the gas flow to enter and/orexit non-axially to and from the fins 104 and then turn axially insidethe fins 104 which results in an increased pressure drop. The anodecooler heat exchanger 100 may be fabricated with either the fingerplates 102 a, 102 b or the end caps 102 c located on either end or acombination of both. In other words, for the combination of finger plateand end cap, the top of the fins 104 may contain one of finger plate orend cap, and the bottom of the fins may contain the other one of thefinger plate or end cap.

Hot and cold flow streams 1131, 1133 flow in adjacent corrugations,where the metal of the corrugated sheet 104 separating the flow streamsacts as a primary heat exchanger surface, as shown in FIG. 11A, which isa top cross sectional view of a portion of sheet 104. The sheet 104 maybe relatively thin, such as having a thickness of 0.005 to 0.003 inches,for example 0.012-0.018 inches, to enhance the heat transfer. Forexample, the hot fuel exhaust stream flows inside of the corrugatedsheet 104 (including in the inner recesses of the corrugations) and thecold air inlet stream flows on the outside of the sheet 104 (includingthe outer recesses of the corrugations). Alternatively, the anodeexhaust cooler heat exchanger may be configured so that the fuel exhaustflows on the outside and the air inlet stream on the inside of sheet104. The finger plates 102 a and 102 b prevent the hot and cold flowsfrom mixing as they enter and exit the anode exhaust cooler heatexchanger.

One side (e.g., inner side) of the corrugated sheet is in fluidcommunication with a fuel exhaust conduit which is connected to the fuelexhaust of the solid oxide fuel cell stack and in fluid communicationwith an exhaust conduit from an anode recuperator heat exchanger whichwill be described below. The second side of the corrugated sheet is influid communication with an air inlet stream conduit which will bedescribed in more detail below.

The air inlet stream into the anode exhaust cooler 100 may be directedtoward the centerline of the device, as shown in FIG. 17C.Alternatively, the air inlet stream may have a full or partialtangential component upon entry into the device. Furthermore, ifdesired, an optional baffle plate 101 a or another suitable flowdirector device 101 b may be located over the anode exhaust cooler 100in the air inlet conduit or manifold 33 to increase the air inlet streamflow uniformity across the anode exhaust cooler 100, as shown in FIGS.11B-11D.

FIGS. 11B and 11D illustrate a side cross sectional and semi-transparentthree dimensional views, respectively, of the baffle plate 101 a locatedover the anode exhaust cooler 100 in the air inlet conduit or manifold33. The baffle plate may comprise a cylindrical plate having a pluralityof openings. The openings may be arranged circumferentially in one ormore circular designs and each opening may have a circular or other(e.g., oval or polygonal) shape.

FIG. 11C shows a flow director device 101 b which comprises a series ofoffset baffles 101 c which create a labyrinth gas flow path between thebaffles, as shown by the curved line. If desired, the baffle plate 101 aopenings and/or the baffle 101 c configurations may have an asymmetricor non-uniform geometry to encourage gas flow in some areas of the anodeexhaust cooler and restrict the gas flow in other areas of the anodeexhaust cooler.

FIG. 11D also shows a roughly cylindrical air inlet conduit enclosure 33a having an air inlet opening 33 b. The air inlet conduit or manifold 33is located between the inner wall of enclosure 33 a and the outer wallof the annular anode exhaust conduit 117, as shown in dashed lines inFIG. 11E. Enclosure 33 a also surrounds the anode cooler 100 a toprovide the air inlet stream passages between the fins of plate 104 andthe inner wall of enclosure 33 a.

FIGS. 11D, 11E and 11F also show the fuel inlet conduit 29 whichbypasses the anode exhaust cooler through the central hollow space inthe anode exhaust cooler 100. FIG. 11E is a three dimensional view andFIG. 11F is a three dimensional cut-away view of the device. As shown inFIGS. 11E-11F, the cylindrical corrugated sheet 104 and the disc shapedfinger plates (e.g., 102 b) of the anode cooler 100 have a hollow spacein the middle. The fuel inlet conduit 29 and annular thermal insulation100A are located in this hollow space 100 b (shown in FIG. 10B). Theannular thermal insulation 100 a surrounds the fuel inlet conduit 29 andthermally isolates conduit 29 from the annular anode cooler 100, and theannular fuel (anode) exhaust conduit 117 which surround the insulation100 a, as well as from the annular air inlet conduit or manifold 33which surrounds the annular anode cooler 100, and the annular fuel(anode) exhaust conduit 117. Thus, the fuel inlet stream passes throughthe fuel inlet conduit 29 without substantial heat exchange with thegasses (i.e., fuel exhaust stream and air inlet stream) flowing throughthe anode cooler 100, the fuel exhaust conduit 117 and the air inletconduit or manifold 33. If desired, the fuel inlet conduit may includean optional bellows 29 b with flange 29 c, as shown in FIG. 11E.

As shown in FIGS. 11E-11F, the fuel inlet stream enters the devicethrough the fuel inlet opening 29 a which is connected to the fuel inletconduit 29. The vertical conduit 29 has a horizontal bridging portionconnected to opening 29 a which passes over the air inlet conduit 33 andthe fuel exhaust conduit 117 which are in fluid communication with theanode cooler 100. Thus, the fuel inlet stream is fluidly and thermallyisolated from the air inlet and fuel exhaust streams in and above theanode cooler 100.

Embodiments of the anode exhaust cooler heat exchanger may have one ormore of the following advantages: excellent heat exchange due to minimalmaterial conduction losses between separated flow streams, very compact,light weight, reduced material requirements, reduced manufacturingcosts, elimination of fixture requirements, reduced pressure drop,ability to control flow ratios between two or more flow streams bysimply changing finger plate design. The duty of the anode exhaustcooler heat exchanger may be increased by 20-40% over the prior art heatexchanger. Further, in some embodiments, the anode exhaust cooler heatexchanger may also be shorter than the prior art heat exchanger inaddition to having a higher duty.

Cathode Recuperator Uni-Shell

The cathode recuperator is a heat exchanger in which the air inletstream exchanges heat with the air (e.g., cathode) exhaust stream fromthe fuel cell stack. Preferably, the air inlet stream is preheated inthe anode cooler described above before entering the cathoderecuperator.

The mode of heat transfer through the prior art brazed two finnedcylindrical heat exchanger is defined by that amount of conductive heattransfer that is possible through the brazed assembly of the heatexchange structure. The potential lack of heat transfer can causethermal instability of the fuel cell system and also may not allow thesystem to operate at its rated conditions. The inventors realized thatthe use of a single fin flow separator improves the heat transferbetween fluid streams and provides for a compact heat exchanger package.

An example cathode recuperator 200 uni-shell is illustrated in FIGS. 12Ato 12G. In an embodiment, the three concentric and independent shells A,B and C of FIG. 3C of the prior art structure replaced with a singlemonolithic assembly shown in FIGS. 12A-12B. FIG. 12A shows an explodedthree dimensional view of the assembly components without the heatshield insulation and FIGS. 12B and 12C show three dimensional views ofthe assembly with the components put together and the heat shieldinsulation 202A, 202B installed.

Embodiments of the uni-shell cathode recuperator 200 include a singlecylindrical corrugated fin plate or sheet 304 (shown in FIGS. 12A and12D). The corrugated plate or sheet 304 is preferably ring shaped, suchas hollow cylinder. However, plate or sheet 304 may have a polygonalcross section when viewed from the top if desired. The corrugated plateor sheet 304 is located between inner 202A and outer 202B heat shieldinsulation as shown in FIG. 12C, which is a three dimensional view ofthe middle portion of the recuperator 200, FIG. 12D which is a top viewof the plate or sheet 304, and the FIG. 12E which is a side crosssectional view of the recuperator 200. The heat shield insulation maycomprise hollow cylinders. The heat shield insulation may be supportedby a heat shield shell 204 located below the corrugated plate or sheet304.

In addition to the insulation and the corrugated plate or sheet 304, theuni-shell cathode recuperator 200 also includes a top cap, plate or lid302 a (shown in FIG. 12A) and a similar bottom cap plate or lid (notshown in FIG. 12A for clarity). As shown in FIGS. 12A, 12B, 12F and 12G,in addition to the top cap, plate or lid 302 a, the hot box may alsoinclude a heat shield 306 with support ribs below lid 302 a, a steamgenerator 103 comprising a baffle plate 308 with support ribs supportinga steam coil assembly 310 (i.e., the coiled pipe through which flowingwater is heated to steam by the heat of the air exhaust stream flowingaround the pipe), and an outer lid 312 with a weld ring 313 enclosingthe steam generator 103. A cathode exhaust conduit 35 in outer lid 312exhausts the air exhaust stream from the hot box.

The single cylindrical corrugated fin plate 304 and top and bottom capplates force the air (i.e., cathode) inlet 12314 and air (i.e., cathode)exhaust streams 1227 to make a non-zero degree turn (e.g., 20-160 degreeturn, such as a 90 degree) turn into adjoining hollow fins of the finplate 304 as shown in FIG. 12F (side cross sectional view of theassembly) and 12G (three dimensional view of the assembly). For example,the cathode or air inlet stream flows from the anode cooler 100 to thecathode recuperator 200 through conduit 314 which is located between theheat shield 306 and the top cap 302 a. The air inlet stream flowssubstantially horizontally in an outward radial direction (i.e., in toout radially) as shown by the arrows in FIGS. 12F and 12G until thestream impacts the inner surface of the upper portion of the corrugatedfin plate 304. The impact forces the stream to make a 90 degree turn andflow down (i.e., in an axial direction) in the inner corrugations.Likewise, the hot cathode exhaust stream shown by arrows in FIGS. 12Fand 12G first flows vertically from below through conduit 27 from theATO and is then substantially horizontally in the end portion of conduit27 in a substantially inward radial direction to impact the outersurface of the lower portions of the corrugated fin plate 304. Thiscauses the air exhaust stream to make a non-zero degree turn and flow up(i.e., in an axial direction) in the outer corrugations of plate 304.This single layer fin plate 304 design allows for effective heattransfer and minimizes the thermal variation within the system (from themisdistribution of air).

The use of the cap plates in the cathode recuperator is not required.The same function could be achieved with the use of finger platessimilar to finger plates 102 a, 102 b illustrated for the anode cooler100. The cathode recuperator heat exchanger 200 may be fabricated witheither the finger plates or the end caps located on either end or acombination of both. In other words, for the combination of finger plateand end cap, the top of the fin plate 304 may contain one of fingerplate or end cap, and the bottom of the fins may contain the other oneof the finger plate or end cap

Hot and cold flow streams flow in adjacent corrugations, where the metalof the corrugated plate or sheet 304 separating the flow streams acts asa primary heat exchanger surface, as shown in FIG. 12D, which is a topcross sectional view of a portion of plate or sheet 304. For example,the relatively cool or cold air inlet stream 12314 flows inside of thecorrugated plate or sheet 304 (including in the inner recesses of thecorrugations) and the relatively warm or hot air exhaust stream 1227flows on the outside of the plate or sheet 304 (including the outerrecesses of the corrugations). Alternatively, the air inlet stream 12314may flow on the inside and the air exhaust stream 1227 may flow on theoutside of the corrugated plate or sheet 304.

One side (e.g., outer side) of the corrugated plate or sheet 304 is influid communication with an air exhaust conduit 27 which is connected tothe air exhaust of the solid oxide fuel cell stack and/or the ATOexhaust. The second side of the corrugated plate or sheet 304 is influid communication with a warm air output conduit 314 of the anodecooler 100 described above.

As shown in FIG. 12H, the air inlet stream 1225 exiting the cathoderecuperator 200 may be directed towards the middle lengthwise portion ofa fuel cell stack or column 9 to provide additional cooling in theotherwise hottest zone of the stack or column 9. In other words, middleportion of the fuel cell stack or column 9 is relatively hotter than thetop and bottom end portions. The middle portion may be located betweenend portions of the stack or column 9 such that each end portion extends10-25% of the length of the stack or column 9 and the middle portion is50-80% of the length of the stack or column 9.

The location of the air inlet stream outlet 210 of the recuperator 200can be tailored to optimize the fuel cell stack or column 9 temperaturedistributions. Thus, the vertical location of outlet 210 may be adjustedas desired with respect to vertically oriented stack or column 9. Theoutlet 210 may comprise a circular opening in a cylindrical recuperator200, or the outlet 210 may comprise one or more discreet openingsadjacent to each stack or column 9 in the system.

Since the air inlet stream (shown by dashed arrow in FIG. 12H) exitingoutlet 210 is relatively cool compared to the temperature of the stackor column 9, the air inlet stream may provide a higher degree of coolingto the middle portion of the stack or column compared to the endportions of the stack or column to achieve a higher temperatureuniformity along the length of the stack of column. For example, theoutlet 210 may be located adjacent to any one or more points in themiddle 80%, such as the middle 50%, such as the middle 33% of the stackor column. In other words, the outlet 210 is not located adjacent toeither the top or bottom end portions each comprising 10%, such as 25%such as 16.5% of the stack or column.

Embodiments of the uni-shell cathode recuperator 200 may have one ormore of the following advantages: excellent heat exchange due to minimalmaterial conduction losses between separated flow streams, very compact,light weight, reduced material requirements, reduced manufacturingcosts, reduced pressure drop, provides dead weight as insurance formechanical compression failure. This allows for easier assembly of thefuel cell system, reduced tolerance requirements and easiermanufacturing of the assembly.

Thus, as described above, the anode cooler 100 and the cathoderecuperator 200 comprise “uni-shell” heat exchangers where the processgases flow on the two opposing surfaces of a roughly cylindricalcorrugated sheet. This provides a very short conductive heat transferpath between the streams. The hotter stream (e.g., anode exhaust and ATOexhaust streams in heat exchangers 100, 200, respectively) providesconvective heat transfer to a respective large surface area corrugatedmetal separator sheet 104, 304. Conductive heat transfer then proceedsonly through the small thickness of the separator (e.g., the thicknessof the corrugated sheet 104, 304), and then convective heat transfer isprovided from the sheet 104, 304 to the cooler respective stream (e.g.,the air inlet stream in both heat exchangers 100, 200).

The heat exchangers 100, 200 differ in their approach to manifoldingtheir respective process streams. The roughly cylindrical anode cooler100 uses finger shaped apertures and finger plates 102 a, 102 b to allowa substantially axial entry of the process streams (i.e., the anodeexhaust and air inlet streams) into the corrugated cylindrical sectionof the heat exchanger. In other words, the process streams enter theheat exchanger 100 roughly parallel (e.g., within 20 degrees) to theaxis of the roughly cylindrical heat exchanger.

In contrast, the cathode recuperator 200 includes top and bottom caps302 a, which require the process streams (e.g., the air inlet stream andATO exhaust stream) to enter the heat exchanger 200 roughlyperpendicular (e.g., within 20 degrees) to the axial direction of theheat exchanger 200. Thus, heat exchanger 200 has a substantiallynon-axial process gas entry into the heat exchanger.

If desired, these manifolding schemes may be switched. Thus, both heatexchangers 100, 200 may be configured with the axial process gas entryor non-axial process gas entry. Alternatively, heat exchanger 200 may beconfigured with the axial process gas entry and/or heat exchanger 100may be configured with non-axial process gas entry.

Cathode Recuperator Uni-Shell with Ceramic Column Support and Bellows

In the prior fuel cell systems, it is difficult to maintain a continuousmechanical load on the fuel cell stacks or columns of stacks through thefull range of thermal operating conditions. To maintain a mechanicalload, the prior art systems rely on an external compression system.Embodiments of the present fuel cell system do not include an externalcompression system. The removal of the external compression system,however, can lead to a loss of mechanical integrity of the fuel cellcolumns. The inventors have realized, however, that the externalcompression system can be replaced by an internal compression systemcomprising either a spring loaded or gravity loaded system or acombination of both. The spring loaded system may comprise any suitablesystem, such as a system described U.S. patent application Ser. No.12/892,582 filed on Sep. 28, 2010 and which is incorporated herein byreference in its entirety, which describes an internal compressionceramic spring, and/or or use the uni-shell bellow in conjunction withappropriately tailored thermal expansion of the column and uni-shellmaterial.

In an embodiment shown in FIG. 13A, the uni-shell cathode recuperator200 is located on top of one or more columns 402 to provide additionalinternal compression for the stack or column of stacks 9. The weight ofthe recuperator 200 uni-shell cylinder(s) can act directly on the fuelcell columns 9. With the added weight of the cylinders, the fuel cellcolumns can be prevented from lifting off the hot box base 500 andprovide any required sealing forces. Any suitable columns 402 may beused. For example, the ceramic columns 402 described in U.S. applicationSer. No. 12/892,582 filed on Sep. 28, 2010 and which is incorporatedherein by reference in its entirety may be used.

As discussed in the above described application, the ceramic columns 402comprise interlocked ceramic side baffle plates 402A, 402B, 402C. Thebaffle plates may be made from a high temperature material, such asalumina, other suitable ceramic, or a ceramic matrix composite (CMC).The CMC may include, for example, a matrix of aluminum oxide (e.g.,alumina), zirconium oxide or silicon carbide. Other matrix materials maybe selected as well. The fibers may be made from alumina, carbon,silicon carbide, or any other suitable material. Any combination of thematrix and fibers may be used. The ceramic plate shaped baffle platesmay be attached to each other using dovetails or bow tie shaped ceramicinserts as described in the Ser. No. 12/892,582 application.Furthermore, as shown in FIG. 13A, one or more fuel manifolds 404 may beprovided in the column of fuel cell stacks 9, as described in the Ser.No. 12/892,582 application.

Furthermore, an optional spring compression assembly 406 may be locatedover the fuel cell column 9 and link adjacent ceramic columns 402 whichare located on the opposing sides of the column of fuel cell stacks 9.The assembly 406 may include a ceramic leaf spring or another type ofspring between two ceramic plates and a tensioner, as described in theSer. No. 12/892,582 application. The uni-shell cathode recuperator 200may be located on a cap 408 on top of the assembly 406, which providesinternal compression to the ceramic columns 402 and to the column offuel cell stacks 9.

As discussed above, in the prior fuel cell systems, it is difficult tomaintain a continuous mechanical load on the fuel cell column throughthe full range of thermal operating conditions. In another embodiment,the inventors have realized, however, that by including a bellows 206 onthe vertical cylinders, the weight of the cylinders can rest directly onthe columns. Thus, in another embodiment, as shown in FIGS. 12A and 13B,the uni-shell cathode recuperator 200 may contain an expansion bellows206 on its outer or heat shield shell 204 located below the corrugatedfin plate 304 for additional coefficient of thermal expansion (CTE)matching to that of the stack columns. Furthermore, as shown in FIG. 16,two additional bellows 850, 852 may be located in the anode inlet areaand the anode tail-gas oxidizer (ATO) exhaust area near top of hot boxfor additional CTE matching.

The bellows 206 allows the cathode recuperator 200 cylinders (e.g., 204,304) to remain in contact with the fuel cell stack 9 columns throughoutthe thermal operating conditions. The bellows 206 are designed to deformduring operations such that the forces induced during temperatureincreases overcome the strength of the bellows, allowing the maincontact point to remain at the top of the fuel cell columns.

Embodiments of the recuperator uni-shell may have one or more of thefollowing advantages: improved sealing of air bypass at the top of thecolumns and continuous load on the columns. The continuous load on thecolumns gives some insurance that even with failure of the internalcompression mechanism there would still be some (vertical) mechanicalload on the columns. The use of the expansion bellows 206 within theuni-shell assembly allows for the shell assembly to expand and contractindependently from the main anode flow structure of the system, therebyminimizing the thermo-mechanical effects of the two subassemblies.

Cathode Exhaust Steam Generator Structure

One embodiment of the invention provides steam generator having anincreased duty over that of the prior art steam generator yet having thesame physical envelope. Further, steam generator coils have localeffects on the flow distribution which subsequently carry down into thecathode recuperator and affect the temperature distribution of theentire hot box. Thus, the embodiments of the cathode exhaust steamgenerator are configured allow control over the cathode exhaust streamflow distribution.

In embodiments of the present invention, the steam generator coil 310 islocated in the lid section (e.g., between inner and outer lids 302A and312) of the cathode recuperator 200 to be closer to the higher gradefuel cell stack air or cathode exhaust waste heat, as shown in FIGS.12A, 12F, 12G and 14. Alternatively, the steam generator 103 mayalternatively be located in the exit plenum (vertical portion) of thecathode recuperator 200.

The lid or exit plenum steam generator 103 location allows for arepresentative reduction in the coil length relative to the prior art.To counteract the effect of a varying pressure drop across the coiledsections, an exhaust baffle plate 308 may also be added to support thecoil 310 (the baffle plate 308 and coil 310 are shown upside down inFIG. 14 compared to FIG. 12A for clarity). Support ribs 309 hold thecoil 310 in place under the baffle plate 308. The steam coil 310 may bea partially or fully corrugated tube or a straight tube which has asmaller diameter near the water inlet conduit 30A than near the steamoutlet conduit 30B. The steam coil 310 may have any suitable shape, suchas a spiral coil, or one or more coils with one or more U-turns (i.e., acoil having at least two sections that are bent at an angle of 320-360degrees with respect to each other). The U-turns for successive passesof the coil may be aligned or shifted with respect to teach other.

As shown in FIG. 12F, the baffle plate 308 forces the air exhaust stream1227 travelling substantially vertically in an axial direction from thecathode recuperator 200 through conduit 119 to the steam generator 103to make an additional pass around the coils 310 in the substantiallyhorizontal, inward radial direction before exiting the hot box throughoutlet 35. The cathode exhaust stream travels through the steamgenerator 103 in a space between plate 302A and baffle plate 308 whenthe coils 310 are attached to the bottom of the baffle plate 308 and/orin a space between the baffle plate 308 and outer plate 312 when thecoils 310 are attached to the top of the baffle plate 308. Theadditional pass provides for a uniform flow distribution across thesurface of the corrugated steam coil 310 and within the cathoderecuperator 200.

Embodiments of the steam generator 103 may have one or more of thefollowing advantages: utilization of higher grade heat, more compactrelative to the prior art, easy to manufacture, improved flowdistribution.

Pre-Reformer Tube-Insert Catalyst

In prior art fuel cell systems, the level of pre-reformation of the fuelprior to hitting the fuel cell may need to be fine tuned depending onthe source of the fuel and respective compositions. The prior art steammethane reformer (SMR) shown in FIGS. 1-3 includes a flat tube with flatcatalyst coated inserts. In the prior at design, there is significantflow length available to accommodate a significant amount of catalystshould the need arise. In embodiments of the present invention, there isa limited amount of flow length available for catalyst placement. Thelimited amount of flow length reduces the overall flow path length ofthe fuel, thus reducing the pressure drop and mechanical designcomplexity needed to have multiple turn flow paths.

In one embodiment of the present invention, the reformer catalyst 137Ais provided into the fuel inlet side of the anode recuperator (e.g.,fuel heat exchanger) 137 in which the fuel exhaust stream is used toheat the fuel inlet stream. Thus, the anode recuperator is a combinedheat exchanger/reformer. For a vertical/axial anode recuperator 137shown in FIG. 15A, the SMR reformation catalyst (e.g., nickel and/orrhodium) 137A may be provided along the entire length of the fuel inletside of the recuperator 137 or just in the lower portion of the fuelinlet side of the recuperator. It could also be comprised of a separateitem following the exhaust of the heat exchanger. It is believed thatthe primary reformation occurs at the bottom of the fuel inlet side ofthe anode recuperator. Thus, the only heat provided to the fuel inletstream in the catalyst 137A containing portion of the anode recuperator137 to promote the SMR reaction is from the heat exchange with the fuelexhaust stream because the anode recuperator is thermally isolated fromthe ATO 10 and stacks 9 by the insulation 10B shown in FIGS. 15A, 16,17B and 18B.

Should additional catalyst activity be desired, a catalyst coated insertcan be inserted into the fuel feed conduits 21 just prior to the fuelcell stacks 9. The fuel feed conduits 21 comprise pipes or tubes whichconnect the output of the fuel inlet side of the anode recuperator 137to the fuel inlet of the fuel cell stacks or columns 9. The conduits 21may be positioned horizontally over the hot box base 500, as shown inFIG. 15A and/or vertically over the hot box base 500, as shown in FIG.15B. This catalyst is a supplement or stand alone feature to thecatalyst coated fin at the bottom of the anode recuperator 137. Ifdesired, the catalyst may be placed in less than 100% of the fuel feedconduits (i.e., the catalyst may be placed in some but not all conduits21 and/or the catalyst may be located in only a part of the length ofeach or some of the conduits). The placement of the SMR catalyst at thebottom of the hot box may also act as a temperature sink for the bottommodules.

FIGS. 15C and 15D illustrate embodiments of catalyst coated inserts 1302a, 1302 b that may be used as anode recuperator/pre-reformer 137 tubeinsert catalyst or as inserts in conduits 21. The catalyst coated insert1302 a has a generally spiral configuration. The catalyst coated insert1302 b includes a series of generally parallel wire rosettes 1304.

Embodiments of the pre-reformer tube-insert catalyst may have one ormore of the following advantages: additional reformation length ifdesired and the ability to place endothermic coupling with the bottommodule of the column should the bottom modules be hotter than desired.

Anode Flow Structure and Flow Hub

FIG. 16 illustrates the anode flow structure according to one embodimentof the invention. The anode flow structure includes a cylindrical anoderecuperator (also referred to as a fuel heat exchanger)/pre-reformer137, the above described anode cooler (also referred to as an airpre-heater) heat exchanger 100 mounted over the anode recuperator, andan anode tail gas oxidizer (ATO) 10.

The ATO 10 comprises an outer cylinder 10A which is positioned aroundthe inner ATO insulation 10B/outer wall of the anode recuperator 137.Optionally, the insulation 10B may be enclosed by an inner ATO cylinder10D, as shown in FIG. 18B. Thus, the insulation 10B is located betweenthe outer anode recuperator cylinder and the inner ATO cylinder 10D. Anoxidation catalyst 10C is located in the space between the outercylinder 10A and the ATO insulation 10B (or inner ATO cylinder 10D ifpresent). An ATO thermocouple feed through 1601 extends through theanode exhaust cooler heat exchanger 100 and the cathode recuperator 200to the top of the ATO 10. The temperature of the ATO may thereby bemonitored by inserting a thermocouple (not shown) through this feedthrough 1601.

An anode hub structure 600 is positioned under the anode recuperator 137and ATO 10 and over the hot box base 500. The anode hub structure iscovered by an ATO skirt 1603. A combined ATO mixer 801/fuel exhaustsplitter 107 is located over the anode recuperator 137 and ATO 10 andbelow the anode cooler 100. An ATO glow plug 1602, which aids theoxidation of the stack fuel exhaust in the ATO, may be located near thebottom of the ATO. Also illustrated in FIG. 16 is a lift base 1604 whichis located under the fuel cell unit. In an embodiment, the lift base1604 includes two hollow arms with which the forks of a fork truck canbe inserted to lift and move the fuel cell unit, such as to remove thefuel cell unit from a cabinet (not shown) for repair or servicing.

FIG. 17A illustrates an anode flow hub structure 600 according to anembodiment. The hub structure 600 is used to distribute fuel evenly froma central plenum to plural fuel cell stacks or columns. The anode flowhub structure 600 includes a grooved cast base 602 and a “spider” hub offuel inlet pipes 21 and outlet pipes 23A. Each pair of pipes 21, 23Aconnects to one of the plurality of stacks or columns. Anode sidecylinders (e.g., anode recuperator 137 inner and outer cylinders and ATOouter cylinder 10A) are then welded or brazed into the grooves in thebase 602 creating a uniform volume cross section for flow distribution,as shown in FIGS. 17B, 17C and 18, respectively. The “spider” fuel tubes21, 23A run from the anode flow hub 600 out to the stacks where they arewelded to vertical fuel rails (see e.g., element 94 in FIG. 1). Theanode flow hub 600 may be created by investment casting and machiningand is greatly simplified over the prior art process of brazing largediameter plates.

As shown in FIGS. 17B and 17C (side cross sectional views) and 17D (topcross sectional view) the anode recuperator 137 includes an innercylinder 139, a corrugated finger plate or cylinder 137B and an outercylinder 137C coated with the ATO insulation 10B. FIG. 17B shows thefuel inlet flow 1729 from fuel inlet conduit 29 which bypasses the anodecooler 100 through its hollow core, then between the cylinders 139 and137B in the anode recuperator 137 and then to the stacks or columns 9(flow 1721) (shown also in FIG. 20) through the hub base 602 andconduits 21. FIG. 17C shows the fuel exhaust flow 1723A from the stacksor columns 9 through conduits 23A into the hub base 602, and from thehub base 602 through the anode recuperator 137 between cylinders 137Band 137C into the splitter 107. One part of the fuel exhaust flow streamfrom the splitter 107 flows through the above described anode cooler 100while another part flows from the splitter 107 into the ATO 10. Anodecooler inner core insulation 100A may be located between the fuel inletconduit 29 and the bellows 852/supporting cylinder 852A located betweenthe anode cooler 100 and the ATO mixer 801, as shown in FIGS. 16, 17Band 17C. This insulation minimizes heat transfer and loss from the anodeexhaust stream in conduit 31 on the way to the anode cooler 100.Insulation 100A may also be located between conduit 29 and the anodecooler 100 to avoid heat transfer between the fuel inlet stream inconduit 29 and the streams in the anode cooler 100. Furthermore,additional insulation may be located around the bellows 852/cylinder852A (i.e., around the outside surface of bellows/cylinder) if desired.

FIG. 17C also shows the air inlet flow from conduit 33 through the anodecooler 100 (where it exchanges heat with the fuel exhaust stream) andinto the cathode recuperator 200 described above.

Embodiments of the anode flow hub 600 may have one or more of thefollowing advantages: lower cost manufacturing method, ability to usefuel tube in reformation process if required and reduced fixturing.

ATO Air Swirl Element

In another embodiment of the invention, the present inventors realizedthat in the prior art system shown in FIGS. 1-9, the azimuthal flowmixing could be improved to avoid flow streams concentrating hot zonesor cold zones on one side of the hot box 1. Azimuthal flow as usedherein includes flow in angular direction that curves away in aclockwise or counterclockwise direction from a straight linerepresenting a radial direction from a center of a cylinder to an outerwall of the cylinder, and includes but is not limited to rotating,swirling or spiraling flow. The present embodiment of the inventionprovides a vane containing swirl element for introducing swirl to theair stream provided into the ATO 10 to promote more uniform operatingconditions, such as temperature and composition of the fluid flows.

As shown in FIGS. 18A, 18B and 18C, one embodiment of an ATO mixer 801comprises a turning vane assembly which moves the stack air exhauststream heat azimuthally and/or radially across the ATO to reduce radialtemperature gradients. The cylindrical mixer 801 is located above theATO 10 and may extend outwardly past the outer ATO cylinder 10A.Preferably, the mixer 801 is integrated with the fuel exhaust splitter107 as will be described in more detail below.

FIG. 18B is a close up, three dimensional, cut-away cross sectional viewof the boxed portion of the ATO 10 and mixer 801 shown in FIG. 18A. FIG.18C is a three dimensional, cut-away cross sectional view of theintegrated ATO mixer 801/fuel exhaust splitter 107.

As shown in FIG. 18A, the turning vane assembly ATO mixer 801 maycomprise two or more vanes 803 (which may also be referred to asdeflectors or baffles) located inside an enclosure 805. The enclosure805 is cylindrical and contains inner and outer surfaces 805A, 805B,respectively (as shown in FIG. 18C), but is generally open on top toreceive the cathode exhaust flow from the stacks 9 via air exhaustconduit or manifold 24. The vanes 803 may be curved or they may bestraight. A shape of turning vane 803 may curve in a golden ratio arc orin catenary curve shape in order to minimize pressure drop per rotationeffect.

The vanes 803 are slanted (i.e., positioned diagonally) with respect tothe vertical (i.e., axial) direction of the ATO cylinders 10A, 10D, atan angle of 10 to 80 degrees, such as 30 to 60 degrees, to direct thecathode exhaust 1824 in the azimuthal direction. At the base of eachvane 803, an opening 807 into the ATO 10 (e.g., into the catalyst 10Ccontaining space between ATO cylinders 10A and 10D) is provided. Theopenings 807 provide the cathode exhaust 1824 azimuthally from theassembly 801 into the ATO as shown in FIG. 18C. While the assembly 801is referred to as turning vane assembly, it should be noted that theassembly 801 does not rotate or turn about its axis. The term “turning”refers to the turning of the cathode exhaust stream 1824 in theazimuthal direction.

The assembly 801 may comprise a cast metal assembly. Thus, the air exitsthe fuel cell stacks it is forced to flow downwards into the ATO mixer801. The guide vanes 803 induce a swirl into the air exhaust stream 1824and direct the air exhaust stream 1824 down into the ATO. The swirlcauses an averaging of local hot and cold spots and limits the impact ofthese temperature maldistributions. Embodiments of the ATO air swirlelement may improve temperature distribution which allows all stacks tooperate at closer points, reduced thermal stress, reduced componentdistortion, and longer operating life.

ATO Fuel Mixer/Injector

Prior art systems include a separate external fuel inlet stream into theATO. One embodiment of the present provides a fuel exhaust stream as thesole fuel input into the ATO. Thus, the separate external ATO fuel inletstream can be eliminated.

As will be described in more detail below and as shown in FIGS. 17C and18C, the fuel exhaust stream 1823B exiting the anode recuperator 137through conduit 23B is provided into splitter 107. The splitter 107 islocated between the fuel exhaust outlet conduit 23B of the anoderecuperator 137 and the fuel exhaust inlet of the anode cooler 100(e.g., the air pre-heater heat exchanger). The splitter 107 splits thefuel exhaust stream into two streams. The first stream 18133 is providedto the ATO 10. The second stream is provided via conduit 31 into theanode cooler 100.

The splitter 107 contains one or more slits or slots 133 shown in FIGS.18B and 18C, to allow the splitter 107 functions as an ATO fuelinjector. The splitter 107 injects the first fuel exhaust stream 18133in the ATO 10 through the slits or slots 133. A lip 133A below the slits133 and/or the direction of the slit(s) force the fuel into the middleof the air exhaust stream 1824 rather than allowing the fuel exhauststream to flow along the ATO wall 10A or 10D. Mixing the fuel with theair stream in the middle of the flow channel between ATO walls 10A and10D allows for the highest temperature zone to be located in the flowstream rather than on the adjacent walls. The second fuel exhaust streamwhich does not pass through the slits 133 continues to travel upwardinto conduit 31, as shown in FIG. 17C. The amount of fuel exhaustprovided as the first fuel exhaust stream into the ATO through slits 133versus as the second fuel exhaust stream into conduit 31 is controlledby the anode recycle blower 123 speed (see FIGS. 17C and 20). The higherthe blower 123 speed, the larger portion of the fuel exhaust stream isprovided into conduit 31 and a smaller portion of the fuel exhauststream is provided into the ATO 10, and vice-versa.

Alternate embodiments of the ATO fuel injector include porous media,shower head type features, and slits ranging in size and geometry.

Preferably, as shown in FIG. 18C, the splitter 107 comprises an integralcast structure with the ATO mixer 801. The slits 133 of the splitter arelocated below the vanes 803 such that the air exhaust stream which isazimuthally rotated by the vanes while flowing downward into the ATO 10provides a similar rotation to the first fuel exhaust stream passingthrough the slits 133 into air exhaust steam in the ATO. Alternatively,the splitter 107 may comprise a brazed on ring which forms the ATOinjector slit 133 by being spaced apart from its supporting structure.

Cathode Exhaust Swirl Element

Stacks could also be rotated slightly on their axis such that the facesof the stacks which face the middle of the ring of stacks do not alignradially, but are positioned with respect to each other at a slight,non-zero angle, such as 1 to 20 degrees for example. This may create aslight swirl to the cathode exhaust stream (i.e., air) leaving thestacks moving in towards the central axis of the hot box. The advantageof this swirl effect is the blending of cathode exhaust temperaturesfrom column to column resulting in more uniform temperaturedistribution. FIG. 18D illustrates the top view of the fuel cell systemof FIG. 3A where the stacks 14 are rotated such that the faces 14 a ofthe stacks which face the middle of the ring of stacks of the stacks donot align radially. In other words, the faces 14 a shown by dashed linesare not tangential to the circle which forms the interior of the ring ofstacks 14, but deviate from the tangent by 1-20 degrees.

Stack Electrical Terminals and Insulation

The prior art system includes current collector rods that penetrate theanode base plate and the hot box base plates through severalfeedthroughs. Each feed through has a combination of ceramic andmetallic seal elements. Multiple plate penetrations, however, requiresealing of current collector rods at each plate to prevent leakagebetween inlet and exhaust air streams and overboard air leakage from theexhaust stream. Any leakage, however, reduces the overall efficiency ofthe hot box and may cause localized thermal imbalances.

An embodiment of a simplified stack electrical terminal (e.g., currentcollector rod 950) is illustrated in FIGS. 16 and 19. In thisembodiment, the stack support base 500 contains a bridging tube 900which eliminates the need for one of the seal elements. The bridgingtube 900 may be made of an electrically insulating material, such as aceramic, or it may be made of a conductive material which is joined to aceramic tube outside the base pan 502. The use of a bridging tube 900eliminates the air in to air out leak path. The currentcollector/electrical terminal 950 is routed in the bridging tube 900from top of the cast hot box base 500 through the base insulation 501and out of the base pan 502. A sheet metal retainer 503 may be used tofix the tube 900 to the base pan 502.

The tube 900 may be insulated in the base with super wool 901 and/or a“free flow” insulation material 902. The “free flow” insulation 902 is afluid that can be poured into an opening in the base 500 around the tube900 but solidifies into a high temperature resistant material whencured.

Embodiments of the simplified stack electrical terminals may have one ormore of the following advantages: elimination of the cross over leakrisk and reduced cost due to elimination of repeat sealing elements andimproved system efficiency by reduced air losses.

In an alternative embodiment, the ATO insulation 10B and the anodecooler inner core insulation 100A (shown in FIG. 16A) may also comprisethe free flow insulation. Furthermore, an outer cylinder 330 may beconstructed around the outer shell of the hot box as shown in FIG. 12A.The gap between outer cylinder 330 and the outer shell of the hot boxmay then be filled with the free flow insulation. The outer shell of thehot box forms the inner containment surface for the free flowinsulation.

Process Flow Diagram

FIG. 20 is a schematic process flow diagram representation of the hotbox 1 components showing the various flows through the componentsaccording to another embodiment of the invention. The components in thisembodiment may have the configuration described in the prior embodimentsor a different suitable configuration. In this embodiment, there are nofuel and air inputs to the ATO 10.

Thus, in contrast to the prior art system, external natural gas oranother external fuel is not fed to the ATO 10. Instead, the hot fuel(anode) exhaust stream from the fuel cell stack(s) 9 is partiallyrecycled into the ATO as the ATO fuel inlet stream. Likewise, there isno outside air input into the ATO. Instead, the hot air (cathode)exhaust stream from the fuel cell stack(s) 9 is provided into the ATO asthe ATO air inlet stream.

Furthermore, the fuel exhaust stream is split in a splitter 107 locatedin the hot box 1. The splitter 107 is located between the fuel exhaustoutlet of the anode recuperator (e.g., fuel heat exchanger) 137 and thefuel exhaust inlet of the anode cooler 100 (e.g., the air pre-heaterheat exchanger). Thus, the fuel exhaust stream is split between themixer 105 and the ATO 10 prior to entering the anode cooler 100. Thisallows higher temperature fuel exhaust stream to be provided into theATO than in the prior art because the fuel exhaust stream has not yetexchanged heat with the air inlet stream in the anode cooler 100. Forexample, the fuel exhaust stream provided into the ATO 10 from thesplitter 107 may have a temperature of above 350 C, such as 350-500 C,for example 375 to 425 C, such as 390-410 C. Furthermore, since asmaller amount of fuel exhaust is provided into the anode cooler 100(e.g., not 100% of the anode exhaust is provided into the anode coolerdue to the splitting of the anode exhaust in splitter 107), the heatexchange area of the anode cooler 100 described above may be reduced.

The splitting of the anode exhaust in the hot box prior to the anodecooler has the following benefits: reduced cost due to the smaller heatexchange area for the anode exhaust cooler, increased efficiency due toreduced anode recycle blower 123 power, and reduced mechanicalcomplexity in the hot box due to fewer fluid passes.

The benefits of eliminating the external ATO air include reduced costsince a separate ATO fuel blower is not required, increased efficiencybecause no extra fuel consumption during steady state or ramp to steadystate is required, simplified fuel entry on top of the hot box next toanode gas recycle components, and reduced harmful emissions from thesystem because methane is relatively difficult to oxidize in the ATO. Ifexternal methane/natural gas is not added to the ATO, then it cannotslip.

The benefits of eliminating the external ATO fuel include reduced costbecause a separate ATO air blower is not required and less ATOcatalyst/catalyst support is required due to higher average temperatureof the anode and cathode exhaust streams compared to fresh external fueland air streams, a reduced cathode side pressure drop due to lowercathode exhaust flows, increased efficiency due to elimination of thepower required to drive the ATO air blower and reduced main air blower125 power due to lower cathode side pressure drop, reduced harmfulemissions since the ATO operates with much more excess air, andpotentially more stable ATO operation because the ATO is always hotenough for fuel oxidation after start-up.

The hot box 1 contains the plurality of the fuel cell stacks 9, such asa solid oxide fuel cell stacks (where one solid oxide fuel cell of thestack contains a ceramic electrolyte, such as yttria stabilized zirconia(YSZ) or scandia stabilized zirconia (SSZ), an anode electrode, such asa nickel-YSZ or Ni-SSZ cermet, and a cathode electrode, such aslanthanum strontium manganite (LSM)). The stacks 9 may be arranged overeach other in a plurality of columns as shown in FIG. 13A.

The hot box 1 also contains a steam generator 103. The steam generator103 is provided with water through conduit 30A from a water source 104,such as a water tank or a water pipe (i.e., a continuous water supply),and converts the water to steam. The steam is provided from generator103 to mixer 105 through conduit 30B and is mixed with the stack anode(fuel) recycle stream in the mixer 105. The mixer 105 may be locatedinside or outside the hot box of the hot box 1. Preferably, thehumidified anode exhaust stream is combined with the fuel inlet streamin the fuel inlet line or conduit 29 downstream of the mixer 105, asschematically shown in FIG. 20. Alternatively, if desired, the fuelinlet stream may also be provided directly into the mixer 105, or thesteam may be provided directly into the fuel inlet stream and/or theanode exhaust stream may be provided directly into the fuel inlet streamfollowed by humidification of the combined fuel streams.

The steam generator 103 is heated by the hot ATO 10 exhaust stream whichis passed in heat exchange relationship in conduit 119 with the steamgenerator 103, as shown in FIG. 12F.

The system operates as follows. The fuel inlet stream, such as ahydrocarbon stream, for example natural gas, is provided into the fuelinlet conduit 29 and through a catalytic partial pressure oxidation(CPOx) 111 located outside the hot box. During system start up, air isalso provided into the CPOx reactor 111 through CPOx air inlet conduit113 to catalytically partially oxidize the fuel inlet stream. Duringsteady state system operation, the air flow is turned off and the CPOxreactor acts as a fuel passage way in which the fuel is not partiallyoxidized. Thus, the hot box 1 may comprise only one fuel inlet conduitwhich provides fuel in both start-up and steady state modes through theCPOx reactor 111. Therefore a separate fuel inlet conduit which bypassesthe CPOx reactor during steady state operation is not required.

The fuel inlet stream is provided into the fuel heat exchanger (anoderecuperator)/pre-reformer 137 where its temperature is raised by heatexchange with the stack 9 anode (fuel) exhaust streams. The fuel inletstream is pre-reformed in the pre-reformer section of the heat exchanger137 (e.g., as shown in FIG. 15A) via the SMR reaction and the reformedfuel inlet stream (which includes hydrogen, carbon monoxide, water vaporand unreformed methane) is provided into the stacks 9 through the fuelinlet conduit(s) 21. As described above with respect to FIGS. 15A and15B, additional reformation catalyst may be located in conduit(s) 21.The fuel inlet stream travels upwards through the stacks through fuelinlet risers in the stacks 9 and is oxidized in the stacks 9 duringelectricity generation. The oxidized fuel (i.e., the anode or fuelexhaust stream) travels down the stacks 9 through the fuel exhaustrisers and is then exhausted from the stacks through the fuel exhaustconduits 23A into the fuel heat exchanger 137.

In the fuel heat exchanger 137, the anode exhaust stream heats the fuelinlet stream via heat exchange. The anode exhaust stream is thenprovided via the fuel exhaust conduit 23B into a splitter 107. A firstportion of the anode exhaust stream is provided from the splitter 107the ATO 10 via conduit (e.g., slits) 133.

A second portion of the anode exhaust stream is recycled from thesplitter 107 into the anode cooler 100 and then into the fuel inletstream. For example, the second portion of the anode exhaust stream isrecycled through conduit 31 into the anode cooler (i.e., air pre-heaterheat exchanger) where the anode exhaust stream pre-heats the air inletstream from conduit 33. The anode exhaust stream is then provided by theanode recycle blower 123 into the mixer 105. The anode exhaust stream ishumidified in the mixer 105 by mixing with the steam provided from thesteam generator 103. The humidified anode exhaust stream is thenprovided from the mixer 105 via humidified anode exhaust stream conduit121 into the fuel inlet conduit 29 where it mixes with the fuel inletstream.

The air inlet stream is provided by a main air blower 125 from the airinlet conduit 33 into the anode cooler heat exchanger 100. The blower125 may comprise the single air flow controller for the entire system,as described above. In the anode cooler heat exchanger 100, the airinlet stream is heated by the anode exhaust stream via heat exchange.The heated air inlet stream is then provided into the air heat exchanger(cathode recuperator 200) via conduit 314 as shown in FIGS. 12F and 20.The heated air inlet stream is provided from heat exchanger 200 into thestack(s) 9 via the air inlet conduit and/or manifold 25.

The air passes through the stacks 9 into the cathode exhaust conduit 24and through conduit 24 and mixer 801 into the ATO 10. In the ATO 10, theair exhaust stream oxidizes the split first portion of the anode exhauststream from conduit 133 to generate an ATO exhaust stream. The ATOexhaust stream is exhausted through the ATO exhaust conduit 27 into theair heat exchanger 200. The ATO exhaust stream heats air inlet stream inthe air heat exchanger 200 via heat exchange. The ATO exhaust stream(which is still above room temperature) is then provided from the airheat exchanger 200 to the steam generator 103 via conduit 119. The heatfrom the ATO exhaust stream is used to convert the water into steam viaheat exchange in the steam generator 103, as shown in FIG. 12F. The ATOexhaust stream is then removed from the system via the exhaust conduit35. Thus, by controlling the air inlet blower output (i.e., power orspeed), the magnitude (i.e., volume, pressure, speed, etc.) of airintroduced into the system may be controlled. The cathode (air) andanode (fuel) exhaust streams are used as the respective ATO air and fuelinlet streams, thus eliminating the need for a separate ATO air and fuelinlet controllers/blowers. Furthermore, since the ATO exhaust stream isused to heat the air inlet stream, the control of the rate of single airinlet stream in conduit 33 by blower 125 can be used to control thetemperature of the stacks 9 and the ATO 10.

Thus, as described above, by varying the main air flow in conduit 33using a variable speed blower 125 and/or a control valve to maintain thestack 9 temperature and/or ATO 10 temperature. In this case, the mainair flow rate control via blower 125 or valve acts as a main systemtemperature controller. Furthermore, the ATO 10 temperature may becontrolled by varying the fuel utilization (e.g., ratio of currentgenerated by the stack(s) 9 to fuel inlet flow provided to the stack(s)9). Finally the anode recycle flow in conduits 31 and 117 may becontrolled by a variable speed anode recycle blower 123 and/or a controlvalve to control the split between the anode exhaust to the ATO 10 andanode exhaust for anode recycle into the mixer 105 and the fuel inletconduit 29.

Any one or more features of any embodiment may be used in anycombination with any one or more other features of one or more otherembodiments. The construction and arrangements of the fuel cell system,as shown in the various exemplary embodiments, are illustrative only.Although only a few embodiments have been described in detail in thisdisclosure, many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Someelements shown as integrally formed may be constructed of multiple partsor elements, the position of elements may be reversed or otherwisevaried, and the nature or number of discrete elements or positions maybe altered or varied. The order or sequence of any process, logicalalgorithm, or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes andomissions may also be made in the design, operating conditions andarrangement of the various exemplary embodiments without departing fromthe scope of the present disclosure.

The invention claimed is:
 1. A method of insulating a fuel cell hot boxfeature comprising: pouring a flowable insulating material into a gapbetween the fuel cell hot box feature and an adjacent feature; andallowing the flowable insulating material to solidify, wherein the hotbox feature comprises a bridging tube containing a current collector andthe adjacent feature comprises a fuel cell stack support base; whereinthe bridging tube extends from under the fuel cell stack support basethrough the flowable insulating material located below the fuel cellstack support base and out of the hot box through a side of a base panbelow the fuel cell stack support base.
 2. The method of claim 1,wherein the gap between the fuel cell hot box feature and the adjacentfeature comprises an “L” shape.
 3. The method of claim 2, furthercomprising adding an insulating wool in end portions in the gap betweenthe fuel cell hot box feature and the adjacent feature.
 4. The method ofclaim 1, further comprising a second hot box feature, wherein the secondhot box feature comprises a cathode recuperator uni-shell comprising amonolithic assembly comprising a single plate; a top enclosure; and abottom enclosure.
 5. The method of claim 1, further comprising aplurality of fuel cell stacks located on the fuel cell stack supportbase.
 6. The method of claim 1, wherein: the bridging tube contains avertical portion located below the fuel cell stack support base and ahorizontal portion connected to the side of the base pan; and theflowable material is located between the fuel cell stack support baseand the horizontal portion of the bridging tube.